[jltsiren]

High density over a large area is a rare exception. Public transit is mostly used in regions that are locally dense but have low-to-moderate population density over the entire region.

Consider a low-density urban area with 1500 people / square km (~4000 people / square mile). You could achieve that with a uniform sprawl of single-family homes on half-acre lots, or with a network of towns / villages / neighborhoods surrounding the city center. The former generates more car traffic, while the latter makes public transit useful for a large fraction of trips. And the latter also makes local services viable, as there will be enough population within a walking distance.

And if you have a 2+2 lane street with enough bus traffic to justify bus lanes, most of the capacity is in the inner lanes not used by the buses. Urban buses stop frequently, making the traffic flow much worse than in lanes without buses.